McCaskill's office said Joseph Shepard's company took possession of the single-engine Pilatus PC 12/47E a week ago and that it will be used primarily for his business. The plane also will be chartered for use by others by an independent charter company.

The Democratic senator previously faced criticism over another airplane for which she and Shepard had an ownership stake. The plane was sold in 2011, after McCaskill reimbursed the federal treasury $88,000 for taxpayer-funded travel on it and later paid St. Louis County about $320,000 in back property taxes, interest and penalties related to it. The plane was sold for about $1.9 million to Northeast Montana Stat Air Ambulance Cooperative.

McCaskill spokesman John LaBombard said Friday that the senator was publicly and immediately disclosing the plane purchase.

"Any use of the plane by Claire will never be paid with taxpayer dollars, and Joseph has implemented strict safeguards to ensure every cost associated with the plane is paid fully and on time," LaBombard said.

Shepard's company is to file a personal property declaration for the airplane with the tax authority in St. Louis County on Jan. 2. An independent company will manage compliance and monitoring of tax and financial reporting and disclosures.

McCaskill is a former state auditor and won her first U.S. Senate term in 2006. She won re-election in 2012 by defeating Republican U.S. Rep. Todd Akin.